Electron emission device



April 25, 1933.

J. w. MARDEN ET AL ELECTRON EMISSION DEVICE Filed Oct. 27, 1927 2 Sheets-Sheet 1 JW MAEOEN BY E. A. LEoseEE ATTORNEY l6 I i 1 5. U 57 INVENTOR Patented Apr. 25, 1933 UNITED STATES PATENT OFFICE JOHN w. MARDEN AND ERNEST A. LEDERER, OF EAST ORANGE, NEW JERSEY, As- SIGNORS TO WESTINGHOUSE LAMP COMPANY, A CORPORATION or PENNSYLVANIA ELECTRON EMISSION DEVICE Application filed October 27, 1927. Serial No. 228,995.

This invention relates to electron discharge devices such as shown and described in our Patent No. 1,7 95,730 issued March 10, 1931, for Electron emission device.

An object of the resent invention is to provide a device of the above character which may be manufactured in an expeditious and practical manner without the sacrifice of any of the essential characteristics required to make the device useful and desirable.

Another object of the invention is to provide an electron-emission device of the above character so constructed as to facilitate the heat treatment of the electrodes.

A further object of the invention is to provide a device of the above character in which certain of the electrodes may be conveniently produced at a minimum cost.

A still further object of the invention is to provide a device of the above character .with electrodes of a simple and practical construction and so arranged as to prevent the detrimental effect of positive ions upon a filament during operation of the device.

Other objects and advantages of the invention will be apparent as the description proceeds.

The present invention aims to provide an improved structure for an electron-emission device, such as a radio tube in which a cathode may be operated at low temperature as, for example, in a device employing an alkali metal.

Radio tubes of the foregoing type, employ a low pressure vapor of an alkali metal such as caesium and may be termed caesium tubes. The alkali metal under certain conditions, greatly increases the electron-emission of a heated cathode such as tungsten, particularly at a temperature so low, that in the absence of the vapor, no substantial electronemission from the tungsten alone would occur. The desirable results obtained are believed to be due to the continuous formation on the tungsten filament or cathode of an adsorbed film which resists evaporation at a temperature far above the vaporization point of the alkali metal. The formation of the adsorbed film is greatly facilitated by the introduction of certain gases having sultable properties, the action being, that if the atoms of certain gases strike the heated electrodes, they form an adsorbed film thereon of substantially atomic thickness which is capable of holding on the atoms of the alkali metal more strongly than does the surface of the heated cathode.

In radio tubes of the above character, it has been the practice to use a vane arrangement of grid and anode elements which consists of strips of metal supported perpendicularly to a plane transverse to the longitudinal axis of the tube and parallel to each otherv with their edges presented to the cathode, as for example, as shown in British Patent 240,850. This arrangement of the elements is not only complicated to produce but presents difficulties when the operation of treating out the gas from the elements is to be performed, since the plates and grids have heretofore not been supported in such fashion that induction heating could be employed to the best advantage.

In the present invention, an electron-emission device of the above character is provided, in which the grid and plate elements are each composed of a plurality of members and either the plate or the grid may be so formed as to lend itself to high frequency induction heating and so disposed with respect to the adjacent element as to heat the same by radiation. It has also been found that the detrimental effect of bombardment by electrons or ions of the bulb and glass beads of the mount structure may be avoided by providing suitable metallic shields.

The plate of the present device may con- ,sist of a ladder-like structure comprising a plurality of strips or slat-like members of nickel, iron, molybdenum, or the like, supported by suitable connector members. The strips may be positioned in spaced relation and transverse to the longitudinal axis of the device and edgewise with-respect to a suitable supported filament.

In accordance with the present invention, the grid electrode may be of the same general construction as the plate and may be in the form of a ladder-like enclosure comprised of two sets or series of oppositely disposed vanes in the form of metallic strips so arranged as to be dis osed m pans n spaced relation, the mem ers of each pair occupying the same horizontal plane. The ends of the vanes may be secured to a connector or support-member. With this arrangement an enclosure having a plurality of oppositely disposed vanes is provided.

I Each pair of vanes is disposed with one of its longer edges opposite to the longer edge of another vane. This arrangement provides a rid in which a filament may be disposed adjacent to the edges of the plurality of oppositely disposed vanes. Inasmuch as the ends or side walls of the enclosing grid structure are continuous with the vanes, the grid is adapted for efi'ective heating by means of high frequency induction.

The plate element employed is preferably formed of two members disposed on opposite sides of the grid. Each of the plate members as above mentioned constitutes a plurality of vanes arranged in spaced relation in a manner similar to the vanes of the grid. The vanes are connected at their ends by connector or support-members and a plate or shield in the form of a metallic sheet" of metal is disposed on one side of each of the series of vanes which constitute the plate or anode. When in position with respect to the grid, the anode is so arranged that the vanes thereof are interposed between or in overlap ing relation to the vanes of the grid. When lie plate or anode is in position with relation to the grid, the vanes of the plate usually extend into the spaces between the vanes of the grid.

It is preferable to provide two plate-mem- 40 bers to constitute an anode and to dispose one plate-member on each side and in similar relation to the grid. The grid electrode andthe two plate-members constituting the anode may be suitably supported 'by support-members extending up from a press in which they are secured. As above mentioned, grid and plate electrodes have heretofore been'provided employing a slat-like structure, such electrodes have been in the form of vanes or slats arranged vertically and in planes radiating from a oommon axis. With this structure, it has been the practice to employ a coiled filament. 'With this structure only a single length of filament was practical and since it is desirable to obtain the greatest effective filament area possible, it will be obvious that with a construction wherein the filament was confined to a given tubular aperture as provided by such electrodes, the filament would necessarily be limited to the length of the aperture provided. The use of a coiled filament, however, in radio tubes is undesirable on account of microphonic effects and for other reasons.

In the present construction, it is possible to use a greater length of filament as, for example, one of angular form such as an inverted V or M-shaped filament and thereby the necessity of coiling the filament is eliminated. It will also .be' appreciated that when using a straight or uncoiled filament the efi'ective area of the filament presented to the plate is greater in proportion to the amount of filament used than is possible with the coiled filament.

The invention will be more clearly'understood by reference to the accompanying drawings in which:

Fig. 1 is a side view of an electron discharge device showing the bulb broken away and a mount embodylng the present invention, a portion of the mount being removed to show its internal structure;

Fig. 1a is a perspective view of the mount 85 shown in Fig. 1, portions being broken away to show the internal structure.

Fig. 2 is a perspective fragmentary view of a mount. made in accordance with the present invention;

Fig. 3 is a plan view of the electrode elements of the mount shown in Fig. 2;

Fig. 4 is a side elevational view of the mount; and,

Fig. 5 is a fragmentary view of the mount 95 shown in Fig. 4 and includes a shield for the press.

Although the invention is described and illustrated as applied to a radio tube of the class hereinbefore described, it is obvious that the present improved construction of mount may be employed in connection. with other t es of devices. As's own, the invention is embodied in a deviceincluding a bulb 10 having a flare tube' 11 provided with the usual press 12. Extending from the press area plurality of support-members for securing the several electrodes in osition as will be more clearly hereinafter escribed.

The present embodiment of the invention includes a filament 13, a grid electrode 14 (see Fig. 2) and a plate electrode which is designated as a whole by the numeral 15. This electrode may comprise two plate-members 16 and 17. The electrodes when secured to the support-wires extending from the press constitute a mount 18. Thus, a flare tube 11 having the electrodes mounted thereon may be sealed at 19 to the bulb 10 and the bulb may be exhausted through an exhaust tube 20 which extends from the interior of the flare tube.

Considering the plate element 15, it will be noted that each of the plate-members 16 and 17 thereof is composed of a ladder-like structureincluding a plurality of rungs or vanes 21. These plate-members are of similar construction and the vanes 21 may be in the form of flat metallic strips connected no 'struction, the filament or cathode is at their ends to support-members 22 and 23. The strips are arranged in parallel spaced relation and in planes substantially transverse to the support-members 22 and 23 so that when the plate-members are in posi tion edges of the vanes or run of the ladder-like structure will be positloned toward the filament 13.

The grid-member 14 includes a set of vanes 24 and 25 connected by support-membars 26, 27 and 28, 29 respectively. The support-members are so arranged as to hold the sets of vanes in spaced relation so that the entire structure forms an enclosure and the vanes 24 and 25 which are substantially the same as the vanes 21 of the plate are in the form of fiat strips and are disposed in spaced relation and in planes substantially transverse to the supports 26, 27 and 28, 29.

When arranged in operative relation to constitute a mount, the vanes 21 of the plate and the vanes 24 and 25 of-the id are usually disposed in spaced overlapping relation. As shown in Fig. 4, the vanes of the grid extend into the spaces between the vanes of the plate. By reason of this conrotected from bombardment since the positive ions form in the space between the anode or plate and the control electrode or grid and not between the filament and plate. This construction provides an electric field which draws the ions to the grid, thus preventing them from impact with the cathode. Although the vanes of the plate and grid may be of any desired space relation, it has been found that a spacing of one eighth of an inch gave satisfactory results.

It will be evident that by reason ofthe present construction the operating characteristics of the device may be varied by adjusting the relative positions of the vanes of the grid and plate and that the present construction lends itself to manufacturing conditions wherein it is desirable to have a simple structure which may. be sufficiently flexible to obtain the best operating condltions in the most convenient and practical.

manner.

Although the present construction of grid and plate may be produced in any suitable manner, it has been found preferable to produce the same by stamping the vanes or metallic strips and their connecting supportmembers from a sheet of metal. mode of construction. a sheet of metal may be punched to provide a plurality of crossmembers or strips in the plane of the sheet, and another operation may be performed to bend the strips so that their largest surfaces are in planes substantially at right angles to the end portions or connectors. If desirable, the strips may be at an angle to their support, that is, they may lie in lanes intersecting the supports at an ang e.

By this with its edges bent over and secured at 30 and 31 as shown in Fig. 3, thus providing an enclosing structure. The plate may be composed of two sections of punched and formed sheet metal, the said members being disposed on opposite sides of the grid and suitably held in the required spaced relation as hereinabove setforth.

As shown in Fig. 1, the present construction of plate and grid is employed in connection with what is termed an M-shaped filament 13. This filament is connected at its ends 32 and 33 to arms 34 and 35 secured to a support-member 36, having one end embedded in the pre'ss12 and connected to a conductor 37. The angular or central loop 38 of the filament is connected to a supportmember 39 secured in the p1'ess12 and terminating'in a conductor 40. Although the filament shown is of M-shape, it is to be understood that an inverted V-shape filament may be used or a plurality of the latter may be employed. This type of filament may be termed an angular filament as distinguishing from a single length of coiled filament as heretofore proposed. The upper ends or loops 41 and 42 of the filament are engaged by resilient support-members secured to arms 43 and 44 extending from a glass or other non-conductive bead 45. This head is secured to an upright-member 46, one end of which is attached to a support 47 embedded in the press and connected to a conductor 48. Extending upwardly from the member 47 is a support rod 49 Which is welded or otherwise secured to a plate or shieldmember 50 (See Fig. 2) secured to the platemember 17. This shield acts as a barrier to prevent bombardment of the head 45, the bead being so positioned as to have the shield 50 disposed between the bead and the operating electrodes. The upper end 51 of the u right-member 46 is provided with a crossar 52 connected to a support-member 53 which latter member is secured to a plate or shield 54 secured to the plate-member 16, the lower end of the suppoitmember 53 being secured to .a support 55 embedded in the press 12. The shield 54 prevents bombardment of the walls of the bulb. so that the shields 50 and 54 serve to enclose the elec-- disposed transverse to the press, that is, the

mount may be supported upon its side instead of vertically as shown.

The grid-member 14 may be secured to supports 58 and 59 which extend upwardly from the press 12, the support 59 being connected to a conductor 60. The upper.

ends 61 and 62 of the supports 58 and 59 respectively rnay be connected by brace-. members 63 and 64 which are embedded'in the head so as to give thestructure rigidity. As will be noted, the cross-bar 52 is secured to both the upright-member 46 and the support-rod 49, thus connecting the plate-members and adding to the strength of the mount.

The alkali metal'such as caesium-dichrm mate or caesium permanganate mixed with a reducing agent such as silicon or a mixture of caesium chloride and calcium may be introduced into the bulb 10 in any suitable manner as, for example, by means of an auxiliary communicating tube (not shown) or is preferably generated from a pellet 65 held in a loop 66 provided in a metallicv strip 67, the ends 68 and 69 of the strip being suitably secured to the support 58. The formation of the support for the pellet 65 provides a simple and easy means of introducing and holding it, since the loop which engages the pellet is of a resilient nature and the pellet may be readily intro.-

duced therein and may be heated by high frequency induction to facilitate reduction or liberate the alkali metal.

By reason of the present invention, the efi'ective area of the grid and plate electrodes may be more completely utilized by employing a straight or uncoiled filament and thereby a device may be constructed which is more even in its operation and in which the detrimental microphonic noises are avoided. The construction of the grid and. plate is further desirable from a practical standpoint since during the heat treatment of the electrodes which is performed by high frequency induction heating, the

grid 14 being an enclosedstructure, is readily heated up and owing to the close relation of a considerable area of the plate and the grid, the plate is heated by radiation from the grid so that the operation of heat treating the electrodes may be efi'ectively carried out to drive off the deleterious gases.

As above mentioned in attaining the most satisfactory results in a device of the prescnt character, it is essential to be able to utilize the entire surface or efl'ective area of the filament by presenting as great an amount of eflective filament surface to the other elements as is ossible.

In other devices of invention relates the grid and plate elements were constructed as above mentioned, in the form of vertical slat-like members disposed in planes radiating from a common center and a filament was employed consisting of a wire wound to helical form. It will be obvious that when employing such type of filament only a small amount of the area of the wire will be effective. Since by reason of the space charge efi'ect, no

the type to which this appreciable amount of the electrons will be drawn from the inside of the coil and only the outer or free surface of the coil will be operative to give the desired electron flow.

The lack of electron emission from the in-' side of the coil may be attributed to what may be termed a cloud of electrons forming within the coil. I

In the above described construction wherein it was proposed to use a coiled filament, it was necessary, by reason of the structural arrangement to. usea single length of filament. Therefore, since the use of a plain or uncoiled filamentwould have required a filament of'an excessive or impractical length, the' coiled formation was resorted to in an attempt to attain the desired amount of efiective filament area.

In the present construction, the desired efi'ective filament area may be readily attained since it is possible to utilize a plurality of lengths of filament disposed in operative relation to the grid and plate. This filament may be of saw-toothed or zig-zag construction either in the form of an inverted V or W. Another important advantage of the present filamentary arcombinationof a given number of strands of filament and agiven number of slats or cross-members in the grid and plate and in the relative spacing of these latter elements with respect to the filament. Furthermore, the lament constants may be varied by placing the strands in parallel orin series. Satisfactory results have been obtained with a filament voltage. of one volt and about 30 milliamperes using a filament of inverted .V-shape or by usin two inverted V-shaped filaments in para lel to operate on one volt at 60 milliamperes or two inverted V-shaped filaments may be used in series requiring two volts and 30 milliamperes.

With the present construction the relative positions of the slats or vanes of the plate and grid may be varied. For example, the vanes of the plate may extend between the vanes of the grid predetermined distances depending on the constants desired in the tube. -If the plate vanes, for

instance, are extended a relatively great distance into the spaces between the grid vanes the amplification constant of the tube will 5 be low and the mutual conductance relatively high, while if the plate vanes are entire- 1 without the space between the grid vanes, the amplification factor will be high and the mutual conductance correspondingly lowered.

This flexibility in the arrangement of the structure to attain a variation in the operating characteristics of the tube is made possible by reason of the present combinawith a plurality of lengths of straight fila- ,ment'. The desirability of the above arrangement over that heretofore used is evident, since exceptionally high constants are obtainable for the reason that the mutual conductance of the tube decreases with the temperature and the present type of caesium tubes must have a high mutual conductance at room temperature in order to be useful at lower temperatures.

By reason of the present invention, a tube may be constructed to operate at one volt, 60 milliamperes with an amplification constant of about 7 and a mutual conductance of about 900 at room temperature. Forexample, the present tube operating at 50 Fahrenheit has a mutual conductance of 700 whichis the average value of other standard tubes which operate at higher voltage and greater amperage.

The importance of the present construc tion will, therefore be recognized when it is appreciated that the present invention provides a radio tube which may be operated at an extremely low voltage and with a minimum amount of current and at the same time, having an operative value somewhat above tubes which consume relatively large amounts of electrical energy.

Another advantage attending the use of the present arrangement wherein straight filaments or a plurality of length of straight filaments are employed is found in the use of such filament to produce a practical device in accordance with the method of manufacture as set forth in our copending application Serial No. 237,001 filed December 1, 1927 for production of alkali metal tubes. In accordance with this method, it is preferable to flash the filament in an oxygen atmosphere at 'a temperature of around 2000 C for about one-half minute.

As more fully explained in the above mentioned copending application, this hi h temperature is employed to clean the lament thoroughly of any grease or hydrocarbons or other impurities which might otherwise react with the oxygen or oxide layer formed thereon.

In order to obtain the best results, a heattion of the lattice-like structure together ing of the filament, to the above mentioned high temperature has been found necessary but in devices as heretofore constructed in which the filament was in the form of a single length of coiled wire confined to an elongated aperture, such heating resulted in a buckling of the wire with a consequent short circuiting by contact with the adjacent element such as the grid. With the present construction wherein plain or straight lengths of filament are employed, it has been found convenient and practical to raise the temperature of the filament to the proper degree without distortion as would be detrimental to the operation of the device.

. A radio tube of the present type which operates ata low filament temperature is desirable from an economic standpoint and attempts have been made to produce the same in a practicalmanner at comparatively low cost. Furthermore, it is necessary in the production of a device of the present type to be able to manufacture the same with uni form operating characteristics. In mount constructions for thistype of device, it has heretofore been found that owing to the formation of the grid and plate, thev required uniformity throughout a large volume of manufactured tubes could not be depended upon. In the present invention the elertrodes are so constructed that the values may be readily predetermined and a predetermined arrangement may be followered with the result that the desired uni-' formity is obtained.

Although a preferred embodiment of the invention is shown and described herein, it is to be understood that modifications may i be made therein without departing from the spirit and scope of the invention as set forth in the appended claims.

Whatis claimed is: a

1. A mount for an electron emission device comprising a unitary grid electrode composed of a plurality of oblong metallic strips connected at their ends to supportmembers, said strips being arranged in spaced relation and in planes parallel to each other and transverse to said supportmembers and a two-part plate electrode composed of a plurality of oblong metallic strips connected at their sides to supportmembers, said strips being disposed in spaced relation and in planes parallel to each other and transverse to said supportmembers, means for supporting said grid and plate electrodes with the strips of the respective electrodes disposed in overlapping relation.

2. A mount for an electron emission device comprising a filament and grid condisposed in planes transverse to the sup rtmembers and means for suppo ment adjacent to the edges of sai rungs.

3. A mount for an electron emission device comprising a filament and grid electrode composed of two oppositely disposed enclosing ladder-like structures consisting of a lurality of run connected at their ends 7 y support-mem ers, means for supporting a filament within said grid and a plate member of two oppositely disposed ladder-like structures positioned adjacent to said grid. l

4. A mount for an electron emission device comprising a filament and-grid electrode composed of two oppositely disposed enclosing ladder-like structures consisting of a plurality of run s connected at their ends by support-mam ers, means for supporting a filament within said grid and a pair of plate members each of ladder-like structure, a half disposed on opposite sides of said grid.

5. A mount vice comprising a filament and for an electronemission degrid electrode composed of an enclosing ladder-like structure consisting of a plurality of rungs connected at their ends by support-members, means for supporting a filament within said grid and a plate members of ladder-like construction positioned adjacent to said grid and a shield associated with said plate'member.

6. A mount for an electron emission device comprising a filament and grid electrode composed of an enclosing ladder-like structure consisting of a plurality of rungs connected at their ends by support-members, means for supporting a filament within said grid and a pair of plate members of ladder-like construction disposed on oppo-- site sides of said grid, each of said plate members having a shield in the form of a metallic sheet.-

7. A-mount for an electron emission device comprising a filament and grid electrode composed of an enclosing ladder-like structure consisting of a plurality of rungs connected at their ends by support-members,

' means for supporting a filament within said grid and a plate member of ladder-like construction positioned adjacent to said grid 321d a shield associated with said plate mem- 8. An electron emission device comprising a grid element composed of a plurality of vertical rows of vanes arranged in parallel spaced relation, a plate element composed of a plurality of vertical rows of vanes disposed in parallel spaced relation, a cathode consisting of a plurality of lengths of filament wire and means for supporting said elements in a common vertical plane at the side of said cathode and with the'vanes substantially transverse to said lengths of filament wire.

9.. An electron-emission device comprising a grid element composed of two rows of vanes arranged in parallel spaced relation,

at right angles to said cathode.

10. An electron emission device comprising a plurality of angular filaments and a plurality o'felectrodes each composed of vertical rows of vanes disposed in parallel "spaced relation at one side of and in operative relation to said filaments.

11. An electron emission device comprising a bulb, a grid element consisting of two rowsof vanes, each row including a plurality of vanes disposed in spaced relation, a plate element consisting of two rows of vanes, each row including a plurality ofv vanes disposed in spaced relation, said elements having their respective vanes in overlapping relation, a filament supported in said bulb and means for supporting said elements at opposite sides of said filament and with said vanes substantially transverse to said filament.

12. An electron emission device comprising a ,bulb, a unitary grid element consisting of two rows of vanes, each row including a plurality of vanes disposed in spaced relation, a two-part plate element consisting of a plurality of vanes comprising metallic strips disposed in spaced relation, the vanes of one element being disposed in planes intermediate the planes in which the vanes of the other element are disposed and substantiallytransverse to the longitudinal axis of said bulb.

In testimony whereof, we have hereunto 0 

